Concrete, Gravel and Sand Calculator

Guide

How the amount is worked out

Slab volume = length × width × thickness. Work in feet, then divide cubic feet by 27 to get cubic yards. Add waste, then divide by how much one bag makes.

Example. A 10 × 10 ft slab 4 in thick is 100 sq ft × 0.333 ft = 33.3 cu ft, or 1.235 cubic yards. An 80 lb bag yields about 0.60 cu ft, so that is 55.6 bags, which rounds up to 56 bags before any waste allowance.

Bag yields

Quikrete’s Concrete Mix data sheet gives about 0.60 cu ft for an 80 lb bag, 0.45 cu ft for a 60 lb bag and 0.30 cu ft for a 40 lb bag. These are approximate and assume the water on the bag. The numbers are editable, and your bag’s label is the final word.

Ready-mix or bags?

Roughly, a yard or more is often easier delivered ready-mixed, as mixing dozens of bags by hand is hard work and joins between batches can be weak. Suppliers have their own minimum loads and short-load fees, so call and ask.

Gravel, sand and mulch

Suppliers sell these by volume (cubic yards) or by weight (tons). To go from volume to weight multiply by a density. The densities here are editorial starting points, not standards: gravel and sand vary with moisture and grading, so ask your supplier.

Safety and rules

Before you dig, call 811 (free) so utilities can mark buried lines. Local rules, permits and height limits vary, so check with your city or county. This is not building or structural advice. Footings, slabs for buildings and anything carrying a load may need engineered design and a permit.

Common questions